1. Field of the Invention
The present invention relates to a valve unit for circulating and blocking flowing subjects. In particular, it relates to a paper sheet takeout device which forwards, adsorbs onto a belt, and successively takes out superimposed paper sheets one by one.
2. Description of the Related Art
Heretofore, as a paper sheet takeout device, there has been known a device which runs a perforated belt along mail articles, sucks holes of the belt by a suction nozzle disposed on the backside of the belt to adsorb the mail articles onto the surface of the belt, and takes out the mail articles one by one (e.g., see U.S. Pat. No. 5,391,051). A solenoid valve is attached between the suction nozzles and a vacuum tank.
Thus, to take out the mail articles, the belt is run, and the solenoid valve is opened to adsorb each mail article onto the belt by the suction nozzle. To continuously take out the mail articles, the solenoid valve is periodically closed in accordance with a timing to take out each mail article, thereby forming a gap between the preceding mail article and the subsequent mail article to be taken out.
However, even when the solenoid valve is closed to stop the suction by the suction nozzles, a negative pressure acting on the mail articles cannot immediately be eliminated while the mail articles are adsorbed onto the belt. Therefore, to take out the mail articles at the high speed, even when the belt is run at the high speed and the opening/closing period of the solenoid valve is shortened, the negative pressure actually acting on the mail articles cannot immediately be eliminated, and hence the mail articles cannot be taken out at the high speed while the gap is provided between the mail articles. Moreover, when the negative pressure cannot immediately be eliminated, two mail articles are taken out while superimposed, and hence, superimposed conveyance easily occurs.
FIGS. 21 and 22 show schematic diagrams of a usual conventional solenoid valve 100. FIG. 21 shows that the solenoid valve 100 is opened, and FIG. 22 shows that the solenoid valve 100 is closed.
In general, the solenoid valve 100 has a coil 104 which moves a substantially cylindrical plunger 102 in an axial direction, a substantially cylindrical chamber 106 (shown only in FIG. 21) which contains the plunger 102, and two holes 108a, 109a formed in the bottom of this chamber 106 to connect two pipes 108, 109 to each other. When this solenoid valve 100 is used in the device of Patent Document 1 described above, the two pipes 108, 109 are connected to a suction nozzle and a vacuum tank, respectively.
When this solenoid valve 100 is opened, the coil 104 is energized to draw out the plunger 102 from the chamber 106, so that the two holes 108a, 109a are connected to each other through the chamber 106. On the other hand, when this solenoid valve 100 is closed, the energizing of the coil 104 is stopped to push the plunger 102 into the chamber 106, so that the bottom surface of the plunger 102 closely comes into contact with the bottom of the chamber 106. In consequence, the two holes 108a, 109a are closed to block a flow path 110 which connects the two pipes 108, 109 to each other.
However, this type of solenoid valve 100 is opened or closed by moving the plunger 102 in the axial direction, and hence an inertia is large. In particular, when the diameters of the pipes 108, 109 connected to the solenoid valve 100 are increased to increase the flow rate of air, the diameter of the plunger 102 for closing the holes 108a, 109a also needs to be increased, and the inertia also increases accordingly.
Moreover, when the solenoid valve 100 is opened, the coil 104 is energized to move the plunger 102, but after the movement of the plunger 102, much time is taken until the air flows into the chamber 106 and a constant pressure is reached. Therefore, From the energizing of the coil to the start of air circulation, a response speed is low. Furthermore, when the solenoid valve 100 is closed, the plunger 102 is pushed into the chamber 106 while pressurizing the air having the constant pressure in the chamber 106, and hence the moving speed of the plunger 102 is low. That is, in the conventional solenoid valve 100, the response speed is low, when the coil 104 is energized and when the energizing is stopped.
Therefore, as in the mail article takeout device of U.S. Pat. No. 5,391,051, when the solenoid valve 100 is used between the suction nozzle and the vacuum tank, the mail articles cannot be taken out at the high speed owing to the above problem of the elimination of the negative pressure, and additionally owing to the low response speed of the solenoid valve 100 itself, the takeout speed is lower.
Moreover, when the solenoid valve 100 is used in the mail article takeout device of U.S. Pat. No. 5,391,051, it is difficult to adsorb a heavy mail article having a relatively large size onto the perforated belt. That is, as shown in FIG. 21, when the solenoid valve 100 is open, its structure requires the circulation of the air through a flow path which is bent plural times, and therefore a passage resistance is large, which makes it difficult to increase the flow rate. In consequence, it is difficult to suck a relatively large amount of the air through the suction nozzle, with the result that the heavy mail article is not easily adsorbed.